Work and Friction

[Rolling]

According to the ExamKrackers book one CANNOT use the equation

W=Fdcostheta for FRICTION.

I did a Kaplan problem about a book sliding down an incline, and this is INFACT the exact same equation that was used. Can someone please explain to me how you CANNOT use this equation to get the work done by friction?

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[shaggybill]

I don't completely under it either, but if you look at the bottom of the next page, it says that work done by friction will probably not be in the MCAT. I wouldn't worry about it too much.

 

[inaccensa]

According to the ExamKrackers book one CANNOT use the equation

W=Fdcostheta for FRICTION.

I did a Kaplan problem about a book sliding down an incline, and this is INFACT the exact same equation that was used. Can someone please explain to me how you CANNOT use this equation to get the work done by friction?

Won't u have to find the net force before u apply that equation. In the sense, Fnet = mgsintheta -ukmgcostheta